IKEv2 Fragmentation
draft-ietf-ipsecme-ikev2-fragmentation-05

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Document Type Active Internet-Draft (ipsecme WG)
Last updated 2014-03-12 (latest revision 2013-11-06)
Replaces draft-smyslov-ipsecme-ikev2-fragmentation
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Network Working Group                                         V. Smyslov
Internet-Draft                                                ELVIS-PLUS
Intended status: Standards Track                        November 3, 2013
Expires: May 7, 2014

                          IKEv2 Fragmentation
               draft-ietf-ipsecme-ikev2-fragmentation-05

Abstract

   This document describes the way to avoid IP fragmentation of large
   IKEv2 messages.  This allows IKEv2 messages to traverse network
   devices that don't allow IP fragments to pass through.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on May 5, 2014.

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   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Conventions Used in This Document  . . . . . . . . . . . .  3
   2.  Protocol details . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.2.  Limitations  . . . . . . . . . . . . . . . . . . . . . . .  4
     2.3.  Negotiation  . . . . . . . . . . . . . . . . . . . . . . .  4
     2.4.  Using IKE Fragmentation  . . . . . . . . . . . . . . . . .  5
     2.5.  Fragmenting Message  . . . . . . . . . . . . . . . . . . .  6
       2.5.1.  Selecting Fragment Size  . . . . . . . . . . . . . . .  8
       2.5.2.  PMTU Discovery . . . . . . . . . . . . . . . . . . . .  8
       2.5.3.  Fragmenting Messages containing unencrypted
               Payloads . . . . . . . . . . . . . . . . . . . . . . . 10
     2.6.  Receiving IKE Fragment Message . . . . . . . . . . . . . . 10
       2.6.1.  Changes in Replay Protection Logic . . . . . . . . . . 12
   3.  Interaction with other IKE extensions  . . . . . . . . . . . . 13
   4.  Transport Considerations . . . . . . . . . . . . . . . . . . . 14
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 18
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 18
   Appendix A.  Design rationale  . . . . . . . . . . . . . . . . . . 20
   Appendix B.  Correlation between IP Datagram size and
                Encrypted Payload content size  . . . . . . . . . . . 21
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 22

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1.  Introduction

   The Internet Key Exchange Protocol version 2 (IKEv2), specified in
   [RFC5996], uses UDP as a transport for its messages.  Most IKEv2
   messages are relatively small, usually below several hundred bytes.
   Noticeable exception is IKE_AUTH exchange, which requires fairly
   large messages, up to several kbytes, especially when certificates
   are transferred.  When IKE message size exceeds path MTU, it gets
   fragmented by IP level.  The problem is that some network devices,
   specifically some NAT boxes, don't allow IP fragments to pass
   through.  This apparently blocks IKE communication and, therefore,
   prevents peers from establishing IPsec SA.

   Widespread deployment of Carrier-Grade NATs (CGN) introduces new
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